Tuning Tensile Strain on FinFET

ABSTRACT

A fin field effect transistor (FinFET) having a tunable tensile strain and an embodiment method of tuning tensile strain in an integrated circuit are provided. The method includes forming a source/drain region on opposing sides of a gate region in a fin, forming spacers over the fin, the spacers adjacent to the source/drain regions, depositing a dielectric between the spacers; and performing an annealing process to contract the dielectric, the dielectric contraction deforming the spacers, the spacer deformation enlarging the gate region in the fin.

BACKGROUND

Semiconductor devices are used in a large number of electronic devices,such as computers, cell phones, and others. Semiconductor devicescomprise integrated circuits that are formed on semiconductor wafers bydepositing many types of thin films of material over the semiconductorwafers, and patterning the thin films of material to form the integratedcircuits. Integrated circuits include field-effect transistors (FETs)such as metal oxide semiconductor (MOS) transistors.

One of the goals of the semiconductor industry is to continue shrinkingthe size and increasing the speed of individual FETs. To achieve thesegoals, fin FETs (FinFETs) or multiple gate transistors are used in sub32 nm transistor nodes. FinFETs not only improve areal density, but alsoimprove gate control of the channel.

In some cases, FinFETs have been constructed using a replacement gateprocess. During such process, the FinFET is initially provided withpolysilicon gates, which are better able to withstand the more severeprocessing conditions of the immediately subsequent processingoperations. Thereafter, in later stages of processing when processingconditions are less severe, the polysilicon gates are removed from theFinFET structures and replaced with permanent metal gates.

In recent years, attempts have been made to improve the performance ormanipulate the characteristics of FinFETs with a stressor. Severalmethods of forming these stressors for FinFETs have been proposed orused in fabrication.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIGS. 1-2 illustrate a p-type fin field-effect transistor (FinFET) andan n-type FinFET;

FIG. 3 is a table summarizing the impact of different stress componentson the electron and hole (110/[110]) FinFETs mobility;

FIGS. 4A, 4B, and 5-15 collectively illustrate a method of forming anembodiment n-type FinFET 20 with tunable tensile strain relative to thep-type FinFET;

FIG. 16 is a chart illustrating how subjecting the dielectric in then-type FinFET to the annealing process (i.e., the thermal process)affects gate length of the transistor;

FIGS. 17-20 illustrate the transistors used to generate the data in thechart of FIG. 16;

FIG. 21 illustrates the N-stressor split providing mobility increase forthe n-type FinFET; and

FIG. 22 illustrates an embodiment method of tuning tensile strain in anintegrated circuit (e.g., the n-type FinFET of FIG. 2).

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the embodiments andare not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the present embodiments are discussed in detailbelow. It should be appreciated, however, that the present disclosureprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to embodiments ina specific context, namely a FinFET. The disclosure may also be applied,however, to other integrated circuits, electronic structures, and thelike.

Referring now to FIG. 1, a p-type FinFET 10 is illustrated. As shown,the p-type FinFET 10 (a.k.a., pFET or PMOS) includes a gate 12 disposedover a fin 14 projecting above a silicon (Si) bulk substrate 16 orsilicon-on-insulator (SOI) substrate (not shown). In addition, asource/drain 18 are found at opposing ends of the fin 14 outside thegate 12. In real production, an effective stressor is produced in thep-type FinFET 10 by forming the source/drain 18 using silicon germanium(SiGe).

Referring now to FIG. 2, an n-type FinFET 20 is illustrated. As shown,the n-type FinFET 20 (a.k.a., nFET or NMOS) includes a gate 22 disposedover a fin 24 projecting above a silicon bulk substrate 26 or SOIsubstrate (not shown). In addition, a source/drain 28 are found atopposing ends of the fin 24 outside the gate 22. Unlike the p-typeFinFET 10, an effective stressor is difficult to produce in the n-typeFinFET 20 during real production.

Referring now to both FIGS. 1-2, the p-type FinFET 10 and the n-typeFinFET 20 each define a fin height, H_(fin), a fin width, W_(fin), and agate length, L_(fin). Stress components for the fin height, T_(fH), thefin width, T_(fW), and the source-drain, T_(fL), direction for the twotransistors are shown in the device coordinate system (DCS). Inaddition, the silicon crystal coordinate system (CCS) for the twotransistors is also depicted.

Referring now to FIG. 3, a table 30 summarizing the impact of differentstress components on the electron and hole (110/[110]) FinFETs mobilityis provided. As highlighted, the electron mobility increases and thehole mobility decreases when the tensile strain in increased in thesource-drain, T_(fL), direction. Therefore, an n-type FinFET 20 with astressor configured to provide sufficient tensile strain in thesource-drain, T_(fL), direction would be beneficial.

Referring collectively to FIGS. 4-15, a method of forming an embodimentn-type FinFET 20 with tunable tensile strain is illustrated relative tothe p-type FinFET 10. Referring now to FIG. 4, the method generallybegins with fin patterning. In an embodiment, both the fins 36 and thesubstrate 34 are formed from silicon. However, the fins 36 and substrate34 may be formed from a variety of suitable semiconductor materials,such as Ge, SiGe, or III-V material.

After the fins 36 have been formed, an oxide deposition process isperformed to generate the shallow trench isolation (STI) regions 38 onopposing sides of the fins 36. Thereafter, a chemical-mechanicalpolishing (CMP) process is performed to smooth the top surface of thedevice. Next, the hard mask 32 shown in FIG. 4 is removed. In anembodiment, the hard mask 32 was formed from two layers, namely anitride layer over an oxide layer.

After the hard mask 32 has been removed, a well implantation and anannealing step are performed. Thereafter, a dummy gate oxide 40 (i.e.,IO OX) (see FIG. 7) is deposited. Once the dummy gate oxide 40 has beendeposited, a polysilicon layer 42 is deposited and patterned using ahard mask 44 as shown in FIG. 5. Next, a lightly doped drain (LDD)implantation process and an annealing process are performed.

Still referring to FIG. 5, after the LDD implantation and annealingsteps, source/drain recessing is performed to provide a place to formthe source/drain regions 46. With recesses having been generated, thesource/drain regions 46 shown in FIG. 5 are epitaxially grown. As shownin FIG. 7, the source/drain regions 46 are disposed on opposing sides ofthe dummy gate oxide 40.

Next, as shown in FIG. 6, a dielectric 48 is formed over thesource/drain regions 46 and the adjacent STI regions 38. In anembodiment, the dielectric 48 is an interlayer dielectric (ILD). In anembodiment, the dielectric 48 is formed using a flowable chemical vapordeposition (FCVD) process.

As shown in FIG. 7, spacers 50 are disposed on opposing sides of thedielectric 48. In an embodiment, the spacers 50 are formed after thepolysilicon layer 42 has been formed. After the dielectric 48 has beenformed, a CMP process is performed to smooth a top surface of thedevice.

Next, referring collectively to FIGS. 6-8, a hard mask 52 is formed overboth the embodiment n-type FinFET 20 (i.e., NMOS) and the neighboringp-type FinFET 10 (i.e., PMOS), which are depicted in an intermediatestage. Thereafter, a portion of the hard mask 52 is selectively removedfrom the n-type FinFET 20 using a photo mask. Next, the polysiliconlayer 42 (see FIG. 5) disposed over the dummy gate oxide 40 and betweentwo of the spacers 50 in the n-type FinFET 20 is removed as representedby the arrow in FIG. 7.

After the polysilicon layer 42 has been removed, an extra annealingprocess is performed. In an embodiment, the extra annealing process isperformed at a temperature of between about 500° C. to about 650° C.,for a time of between about 60 minutes to about 120 minutes, and/or at apressure of about 1 atmosphere. In other embodiments, othertemperatures, times, and pressures may be employed in order to achievedesired results.

In an embodiment, the annealing process causes elements such as, forexample, nitrogen and hydrogen, to be off gassed from dielectric 48 asshown in FIG. 9. When the elements are off gassed, the dielectric 48 inFIG. 9 contracts or shrinks (as represented by the arrows in FIG. 9). Inan embodiment, the annealing process shrinks the dielectric 48 betweenabout 15% to about 18% relative to a size of the dielectric 48 prior tothe annealing process. In an embodiment, the annealing process reduces aheight and a width of the dielectric 48 as shown in FIG. 9 relative tothe dielectric 48 in the p-type FinFET 10 in FIG. 10, which is notsubjected to the extra annealing process.

The contraction or shrinking of the dielectric 48 bends or otherwisedeforms the spacers 50 in the n-type FinFET 20 as shown in FIG. 9.Indeed, the spacers 50 in FIG. 9 are bent or curved inwardly relative tothe straight or unbent spacers 50 in the p-type FinFET 10 in FIG. 10. Inan embodiment, a contour of the contracted dielectric 48 is equivalentto a contour of the spacers 50 in FIG. 9. In an embodiment, thecontracted dielectric 48 is generally vertically aligned with thesource/drain regions 46.

Still referring to FIG. 9, the bending or deformation of the spacers 50in the n-type FinFET 20 laterally expands the gate region 54 of the fin36. Indeed, the spacers 50 are drawn inwardly toward the source/drainregion 46 and each other by the shrinking dielectric 48, which providesadditional surface area where a gate structure may be subsequentlyformed over the fin 36. In other words, an amount of deformation of thespacers 50 is due to the contracted dielectric 48 and contributes to alength of the enlarged gate region 54 in the fin 36. Notably, theenlarged gate region 54 allows for a longer channel in the n-type FinFET20.

In an embodiment, a middle portion of each of the spacers 50 in FIG. 9is deformed more than top and bottom portions of the spacers 50. Inaddition, in an embodiment the spacers 50 in FIG. 9 are laterallyadjacent to the enlarged gate region 54 and the source/drain regions 46.Moreover, in an embodiment the spacers 50 in FIG. 9 are on opposingsides of the contracted dielectric 48.

After the extra annealing process has been performed and the spacers 50of the n-type FET 20 bent or deformed as shown in FIG. 9, the dummy gateoxide 40 in FIG. 9 is removed and the gate electrode structure 56 ofFIGS. 11, 13-14 is constructed. In an embodiment, the gate electrodestructure 56 includes an interfacial oxide 58, a high-k value dielectric60, and a metal gate 62.

After the gate electrode structure 56 has been formed in the n-typeFinFET 20 as shown in FIG. 11, a CMP process is performed to smooth thetop surface of the transistor. Thereafter, a hard mask 64 is formed overboth the embodiment n-type FinFET 20 and the neighboring p-type FinFET10 and then selectively removed from the p-type FinFET 10 using a photomask as shown in FIGS. 11-12. Next, the polysilicon layer 42 disposedover the dummy gate oxide 40 and between two of the spacers 50 in thep-type FinFET 10 of FIG. 12 is removed.

Thereafter, the dummy gate oxide 40 in FIG. 12 is removed and the gateelectrode structure 96 of FIG. 15 is generated. In an embodiment, thegate electrode structure 96 includes an interfacial oxide 98, a high-kvalue dielectric 90, and a metal gate 92 as shown in FIG. 15. After thegate electrode structure 96 has been formed in the p-type FinFET 10 asshown in FIG. 15, a CMP process is performed to smooth the top surfaceof the transistor. In an embodiment, the n-type FinFET 20 and theneighboring p-type FinFET 10 are disposed on the same silicon substrate36 or wafer.

Referring to FIGS. 14-15, it should be recognized that the horizontal orlateral length of the gate region 54 in the n-type FinFET 20 is greaterthan the length of the gate region 94 in the p-type FinFET 10, which hasnot been stretched by shrinking dielectric 48 and inwardly drawn spacers50. In addition, the height of the gate in the n-type FinFET 20 is lessthan the height of the gate in the p-type FinFET 10. In an embodiment,the dielectric 48 in the n-type FinFET 20 is formed from a differentmaterial than the dielectric 48 in the p-type FinFET 10.

Referring now to FIG. 16, a chart 66 illustrating how subjecting thedielectric 48 in the n-type FinFET 20 to the annealing process (i.e.,the thermal process) affects gate length of the transistor.

The n-type FinFETs 70, 74 in FIGS. 19-20 were subjected to an annealingprocess to shrink the dielectric and bend the spacers. The transistor inFIG. 19 was subjected to the extra annealing process at about 600° C.for a period of about 2 hours. The transistor in FIG. 20 was subjectedto an annealing process at about 600° C. for a period of about 1 hour.Thereafter, the gate length of the transistors in FIGS. 19-20 wasmeasured. The average gate length (L_(g)) in the transistor in FIG. 19was measured as 34.3 nm and the average gate length of the transistor inFIG. 20 was measured as 33.6 nm.

Unlike the transistors in FIGS. 19-20, the n-type FinFETs 68, 72 inFIGS. 17-18 were not subjected to the extra annealing process used toshrink the dielectric and bend the spacers. The average gate length(L_(g)) in the transistor in FIG. 17 was measured as 30.4 nm and theaverage gate length of the transistor in FIG. 18 was measured as 31.9nm. Therefore, as shown in the chart 66 in FIG. 16, the average gatelength in the transistor of FIG. 19 increased by about 3.9 nm relativeto the average gate length in the transistor of FIG. 17. Likewise, theaverage gate length in the transistor of FIG. 20 increased by about 1.7nm relative to the average gate length in the transistor of FIG. 18.

Referring now to FIG. 21, a chart 76 indicates that the N-stressor splitshowed mobility increase for the n-type FinFET 20. In FIG. 21, thecircle data points correspond to the transistor with the extra annealingprocess described above while the diamond data points correspond to thetransistor without the benefit of the extra annealing process. When themobility index (I_(dmo)) is plotted relative to the voltage threshold(V_(ts)), the long channel (LC) NMOS mobility increased about 15%.

In FIG. 22, an embodiment method 78 of tuning tensile strain in anintegrated circuit (e.g., the n-type FinFET 20) is illustrated. In block80, a source/drain region is formed on opposing sides of a gate regionin a fin. In block 82, spacers are formed over the fin. The spacers aregenerally adjacent to the source/drain regions. In block 84, adielectric is deposited between the spacers. In block 86, an annealingprocess is performed to contract the dielectric. The dielectriccontraction deforms the spacers, which causes the gate region in the finto enlarge or expand.

An embodiment method of method of tuning tensile strain in an integratedcircuit includes forming a source/drain region on opposing sides of agate region in a fin, forming spacers over the fin, the spacers adjacentto the source/drain regions, depositing a dielectric between thespacers; and performing an annealing process to contract the dielectric,the dielectric contraction deforming the spacers, the spacer deformationenlarging the gate region in the fin.

An embodiment fin field effect transistor (FinFET) having a tunabletensile strain includes a source/drain region on opposing sides of anenlarged gate region in a fin, a contracted dielectric disposed over thesource/drain regions, and spacers disposed over the fin, an amount ofdeformation of the spacers due to the contracted dielectric andcontributing to a length of the enlarged gate region in the fin.

An embodiment integrated circuit having a tunable tensile strainincludes a p-type metal-oxide-semiconductor (PMOS) device with a firstgate region, and an n-type metal-oxide-semiconductor (NMOS) deviceadjacent the PMOS device, the NMOS device including deformed spacers onopposing sides of a contracted dielectric, the deformed spacers adjacenta second gate region, a length of the second gate region greater than alength of the first gate region.

While the disclosure provides illustrative embodiments, this descriptionis not intended to be construed in a limiting sense. Variousmodifications and combinations of the illustrative embodiments, as wellas other embodiments, will be apparent to persons skilled in the artupon reference to the description. It is therefore intended that theappended claims encompass any such modifications or embodiments.

What is claimed is:
 1. A method of tuning tensile strain in anintegrated circuit, comprising: forming a source/drain region onopposing sides of a gate region in a fin; forming spacers over the fin,the spacers adjacent to the source/drain regions; depositing adielectric between the spacers; and performing an annealing process tocontract the dielectric, the dielectric contraction deforming thespacers, the spacer deformation enlarging the gate region in the fin. 2.The method of claim 1, further comprising performing the annealingprocess at a temperature of between about 500° C. to about 650° C. 3.The method of claim 1, further comprising performing the annealingprocess for a time of between about 60 minutes to about 120 minutes. 4.The method of claim 1, further comprising performing the annealingprocess at a pressure of about 1 atmosphere.
 5. The method of claim 1,further comprising performing the annealing process to shrink thedielectric between about 15% to about 18% relative to a size of thedielectric prior to the annealing process.
 6. The method of claim 1,further comprising performing the annealing process to reduce a heightand a width of the dielectric.
 7. The method of claim 1, furthercomprising performing the annealing process to outgas at least one ofnitrogen and hydrogen from the dielectric.
 8. The method of claim 1,further comprising constructing a gate electrode structure over the gateregion as expanded and between the spacers as deformed.
 9. The method ofclaim 1, further comprising contracting the dielectric to draw opposingones of the spacers closer to each other.
 10. The method of claim 1,further comprising deforming the spacer inwardly toward the dielectric,a middle portion of the spacer deformed more than top and bottomportions of the spacer.
 11. A fin field effect transistor (FinFET)having a tunable tensile strain, comprising: a source/drain region onopposing sides of an enlarged gate region in a fin; a contracteddielectric disposed over the source/drain regions; and spacers disposedover the fin, an amount of deformation of the spacers due to thecontracted dielectric and contributing to a length of the enlarged gateregion in the fin.
 12. The FinFET of claim 11, wherein a contour of thecontracted dielectric is equivalent to a contour of the spacers.
 13. TheFinFET of claim 11, wherein the contracted dielectric has been reducedin size about 15% to about 18% relative to an original size of thecontracted dielectric.
 14. The FinFET of claim 11, wherein thecontracted dielectric is vertically aligned with the source/drainregions.
 15. The FinFET of claim 11, wherein the spacers are laterallyadjacent to the enlarged gate region and the source/drain regions and onopposing sides of the contracted dielectric.
 16. The FinFET of claim 11,wherein a gate electrode structure is disposed over the gate region, thegate electrode structure including an interfacial oxide, a high-kdielectric, and a metal gate.
 17. An integrated circuit having a tunabletensile strain, comprising a p-type metal-oxide-semiconductor (PMOS)device with a first gate region; and an n-type metal-oxide-semiconductor(NMOS) device adjacent the PMOS device, the NMOS device includingdeformed spacers on opposing sides of a contracted dielectric, thedeformed spacers adjacent a second gate region, a length of the secondgate region greater than a length of the first gate region.
 18. Theintegrated circuit device of claim 17, wherein a height of a second gatein the NMOS device is less than a height of a first gate in the PMOSdevice.
 19. The integrated circuit device of claim 17, wherein the PMOSdevice includes straight spacers on opposing sides of a dielectric. 20.The integrated circuit device of claim 19, wherein the contracteddielectric and the dielectric are formed from different materials.